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Author Topic: Background Radiation - Could It Be a Vexation ?  (Read 41580 times)
W8JI
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« Reply #60 on: October 28, 2011, 04:42:20 AM »

  The trouble with intermittent VHF parasitic oscillations is that they are not very repeatable.  .  .  The TL-922 has a reputation for occasionally producing a big bang when its ZSAC drops to zero.  At first I thought this was impossible.  However, its the change in I that rings a resonant circuit, so it matters not whether the current went from zero to 180mA or it went from 180mA to 0nA,  either way there is going to briefly be a damped wave 120MHz signal in the 922's anode circuit.  Since there is c. 4300-ohms of XC between the out and in of the 3-500Zs at this freq. regeneration is probably not impossible.
Rich, ag6k

They are only not repeatable for you. That's probably because you blame almost every problem on either a "parasitic", or some bizarre thing like a high energy photon.

For almost everyone else in the world, things can be tested, measured, and confirmed and also follow logical physical behavior.

73 Tom
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W9PMZ
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« Reply #61 on: October 28, 2011, 05:33:31 AM »

As a test engineer who is responsible for the production
of cellular PAs, or for that matter anything else,
to suggest a fix for a problem without having
a failure mode analysis with solid evidence and
resolution I would probably not be employed.

Over the past 30 years I have never had a problem
that did not create repeatable results when the requisite
conditions have been met.

I am obviously not as qualified in tube PA
design as some of the contributors herein,
but I do know that if there is a problem it
can be found and found to be repeatable
when you have found the correct circumstance.

Just my 2 cents...

Regards,

Carl -W9PMZ
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AG6K
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« Reply #62 on: October 28, 2011, 07:43:23 AM »

Quote
Quote from: AG6K on Today at 03:34:22 AM
  The trouble with intermittent VHF parasitic oscillations is that they are not very repeatable.  .  .  The TL-922 has a reputation for occasionally producing a big bang when its ZSAC drops to zero.  At first I thought this was impossible.  However, its the change in I that rings a resonant circuit, so it matters not whether the current went from zero to 180mA or it went from 180mA to 0nA,  either way there is going to briefly be a damped wave 120MHz signal in the 922's anode circuit.  Since there is c. 4300-ohms of XC between the out and in of the 3-500Zs at this freq. regeneration is probably not impossible.
Rich, ag6k


Quote
Tom Rauch: They are only not repeatable for you. That's probably because you blame almost every problem on either a "parasitic", or some bizarre thing like a high energy photon.

  Tom R. has never seen an aurora?

Quote
For almost everyone else in the world, things can be tested, measured, and confirmed and also follow logical physical behavior.

73 Tom

  I've measured the R of VHF suppressor resistors that were paralleled with 8mm Ag-plated Cu strap, and the R had more than tripled after a big bang.  Does it make sense that HF energy could haave done this damage?
Rich, ag6k. 

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AG6K
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« Reply #63 on: October 28, 2011, 08:25:21 AM »

Quote
Carl, W9PHZ:  As a test engineer who is responsible for the production
of cellular PAs, or for that matter anything else,
to suggest a fix for a problem without having
a failure mode analysis with solid evidence and
resolution I would probably not be employed

  Two Hams who have access to spectrum analyzers have tested SB-220s and found that when they are  keyed between Tx and standby with a pulser they produce damped wave energy pulses at c. 110MHz near their anodes.   Nobody who understands spark transmitters should be surprised by this.  On the 3-500Z's tech data sheet it's rated for max input in "Amplifier and Oscillator Service" up to 110MHz.

Quote
Over the past 30 years I have never had a problem
that did not create repeatable results when the requisite
conditions have been met.

I am obviously not as qualified in tube PA
design as some of the contributors herein,
but I do know that if there is a problem it
can be found and found to be repeatable
when you have found the correct circumstance.

  Toyota has  not announced that they found a solution to their rare full-on acceleration problem in vehicles with ABS.  Nissan used to have the same problem but their fix was to disable ABS whenever the throttle was open.  This allows the brakes to lock the wheels and stop the vehicle even at full-throttle.  For owners of  Toyota vehicles with ABS that  experience full-on throttle, the fix is to place the transmission in Neutral, pull over, stop the vehicle, shut it off, and restart.
- note -  Audi GMBH initially had the same problem when they started using ABS on vehicles with computer-controlled throttles.  CBS' 60-Minutes had a segment on it.    Rich, ag6k

Quote
Just my 2 cents...

Regards,

Carl -W9PMZ
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QRP4U2
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Posts: 262




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« Reply #64 on: October 28, 2011, 10:34:37 AM »

I was referring only to the photoelectric effect for the PE formula given, not to the ionization of gas as in a GC.

Quote
How could the exact frequency of a gamma-ray have anything to do with causing conduction Phil?



Because the work function W of the metal has to be overcome by the photon energy in order to give the electron enough energy to travel, as per the equation.

http://physics.about.com/od/quantumphysics/a/photoelectric_2.htm

http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html

Phil - AC0OB
« Last Edit: October 28, 2011, 10:42:03 AM by QRP4U2 » Logged

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QRP4U2
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« Reply #65 on: October 28, 2011, 10:53:12 AM »

Quote
If there is an arc that cannot be explained by some issue with the design of the amplifier itself and cannot be repeated consistently then ether the environment the amplifier is operating in is the cause or some electrical transient exists on the AC mains feeding the amplifier.


Exactly. We have no need to relegate a macro-physical occurrence to some esoteric quantum mechanical theory.

I have seen an accumulation of dust whiskers on a high voltage part of the circuit, such as the final's RF choke or filter cap before the RF choke, cause a momentary arc. Occasional vacuuming cured the problem.  Cheesy

An HV arc outside a tube is similar to lightning; aside from the HV potential it has two other characteristics, light and sound. Light is generated because of the ionization of the gases in the arc channel and the sound is the compression wave from the heating of the ionization channel.

The compression wave may bounce around inside the cabinet and sound worse than it really is.  

This thread has really gotten away from the original question.

Rich, recommend trying one topic at a time and focusing on it, rather than fixating on parasitic oscillations.  Smiley


Phil
« Last Edit: October 28, 2011, 04:54:53 PM by QRP4U2 » Logged

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AF9J
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« Reply #66 on: October 29, 2011, 05:22:51 PM »

Wow!  Some of these posts were hard to read!  Grin

Just my brief, 2 cents worth - Rich, I gather that you think a gamma ray or other high energy photon, hit the tube element, and knocked free an electron, causing an avalanche effect, and a discharge in the tube?  Sorry but the nuclear physics, and quantum mechanics I had for my degree in Nuclear Engineering disagrees with this theory.  For starters the atmosphere is thick enough to attenuate most gamma rays and x-rays (forget about UV - not enough energy in it to do the dirty work).  The cross section (which is a definition for the probability) for collision of gamma rays and X-rays with the materials in a tube, is rather small. So, they really don't have a marked effect on materials, until the flux of them is pretty high.  Could the effect you're postulating, occur with the the low flux levels of gamma rays and x-rays we experience from background radiation?  Sure, BUT, the probability is so low, as to effectively be zero.

I think you'd better look at a another cause.

73,
Ellen - AF9J   
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AG6K
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« Reply #67 on: October 30, 2011, 05:20:05 AM »

Quote
AF9J
   
RE: Background Radiation - Could It Be a Vexation ?
« Reply #66 on: Yesterday at 05:22:51 PM »
   
Wow!  Some of these posts were hard to read!  Grin

Just my brief, 2 cents worth - Rich, I gather that you think a gamma ray or other high energy photon, hit the tube element, and knocked free an electron, causing an avalanche effect, and a discharge in the tube?
  NO.  One more time:  The loosed electrons cause the the tube to briefly conduct.  This pulse of anode-I rings the VHF resonant circuit in the anode whereupon it generats a damped wave VHF signal in the same way that a spark transmitter generated RF.  The feedback-C inside the amplifying device feeds some of the VHF signal back to the input where it can be amplified.  If  VHF gain is high enough, regeneration takes place and a lager amount of VHF energy appears at the anode.  If this energy can not reach the load, it can run amok and cause arcing at the Tune-C or the bandswitch.  This is why the Tune-C in factory-stock SB-220s and TL-922s often has arc-marks. 
- note - the purpose of a VHF suppressor is to reduce VHF amplification to reduce the chance of VHF oscillation.   

Quote
> Sorry but the nuclear physics, and quantum mechanics I had for my degree in Nuclear Engineering disagrees with this theory.

.[/quote]
  Good, it should not agree because you did not understand what I wrote.

 
Quote
For starters the atmosphere is thick enough to attenuate most gamma rays and x-rays (forget about UV - not enough energy in it to do the dirty work).  The cross section (which is a definition for the probability) for collision of gamma rays and X-rays with the materials in a tube, is rather small. So, they really don't have a marked effect on materials,


  So something is wrong with my Geiger-Muller counter?
cheers Ellen.  Rich, ag6k

Quote
until the flux of them is pretty high.  Could the effect you're postulating, occur with the the low flux levels of gamma rays and x-rays we experience from background radiation?  Sure, BUT, the probability is so low, as to effectively be zero.

I think you'd better look at a another cause.

73,
Ellen - AF9J   
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W8JI
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« Reply #68 on: October 30, 2011, 08:54:41 AM »

So now he is apparently claiming:

1.) a tube in cut-off conducts enough to overcome bias from a photon event

2.) this event (that everyone knows is impossible) rings a parasitic circuit

3.) The parasitic causes a vacuum tube that saturates at a few amps to suddenly draw dozens or hundreds of amperes, something it cannot do with emission current no matter what the grid bias

4.) the parasitic is the cause, and not gas, and the parasitic in a tube on standby was trigged by the "photon event"

5.) the compelling evidence this can happen is a Prius automobile's computer system sometimes quits while he is driving 

Did I miss anything?
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AF9J
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« Reply #69 on: October 30, 2011, 09:04:03 AM »

Rich, you're forgetting that a Geiger counter has a gas that will avalanche conduct, much more readily than the (mostly vacuum) that a power tube has.  Also, the collision probability is so low for a gamma ray or x-ray, I don't think you can even count on it 99.99999% of the time.  As it is, for a vacuum tube, you'd probably need hundreds of electrons being released, to have even something close to an avalanche effect in a vacuum tube - not the two, three or four that a typical gamma ray would knock free.  Besides, the collision cross sections of reaction are pretty low.  They're not like the cross sections for low energy neutrons into U235 or PU239.  They're orders of magnitude lower. It's one of the reasons why flux levels and exposure times, for a SPECIFIC AREA of material (not all over it), are what determine when gamma rays become an issue with a material.  Exposure time of a tube to background radiation is one thing, but can you guarantee that the same spot on a tube element, will get hammered with enough random gamma rays, to dump enough electrons at a specific time, to create an avalanche effect?  No.

And Tom, no, you didn't miss Rich's latest postulation.   Wink
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AG6K
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« Reply #70 on: October 30, 2011, 09:41:04 AM »

Quote
W8JI, Tom Rauch
   
RE: Background Radiation - Could It Be a Vexation ?
« Reply #68 on: Today at 08:54:41 AM »
   
Reply with quoteQuote
So now he is apparently claiming:

1.) a tube in cut-off conducts enough to overcome bias from a photon event

  the bias V is still there but electrons get knocked loose when high-energy photons collide with atoms inside the envelope.  This causes electrons to flow if the anode +HV is present. 

Quote
2.) this event (that everyone knows is impossible) rings a parasitic circuit

  I doubt that everyone thinks it impossible that electrons can be knocked loose.

Quote
3.) The parasitic causes a vacuum tube that saturates at a few amps to suddenly draw dozens or hundreds of amperes, something it cannot do with emission current no matter what the grid bias

  Not hundreds of amperes.  TL-922s are known to be able to have a big bang event that damages its VHF parasitic suppressor resistors when the idle current drops from c. 180mA to zero.

Quote
4.) the parasitic is the cause, and not gas, and the parasitic in a tube on standby was trigged by the "photon event"/quote]

  I used to think it impossible but now I'm convinced that a tube can albeit rarely oscillate on standby or do so as it switches from normal ZSAC to standby,  The missing piece of the puzzle was how was the tube able to draw enough current to blow the 1A grid-gnd RFCs when the bias relay contacts are open.  The answer to that is when the tube conducts, the relay contact gap arcs, and since a metal vapor arc has only about 15v-drop.  This still leaves several kV to do mischief.

Quote
[5.) the compelling evidence this can happen is a Prius automobile's computer system sometimes quits while he is driving

  The computer does not quit in the Prius, it gets confused and will not allow the vehicle accelerate at the usual rate - but the vehicle continues on.

Quote
Did I miss anything?

  Mmmmm .  .  .  pretty much everything.  Did you see the aurora in Georgia Tom?
Rich, ag6k
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G3RZP
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« Reply #71 on: October 30, 2011, 09:53:09 AM »

One of the old MIL STD Handbooks (might have been 217) had some data on reliability of tubes under irradiation. Since they were irradiating with neutrons in very large speeds and densities, (which would be more likely to knock electrons out) with tubes under power and got very long lives, it seems more than unlikely.

In any case, to make the parasitic circuit ring with any amplitude, it will need a pretty large current pulse even with a Q of 10. That is not even a few electrons.
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AF6LJ
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« Reply #72 on: October 30, 2011, 10:07:10 AM »

Okay a little perspective here.

If the tube is cut off no current is going to flow if a few thousand electrons are somehow, some way knocked loose. Would this be enough to overcome the bias if the tube is cut off twice or three times past cutoff.?
No it wouldn't. That resonant circuit could have a Q of 5000 and if there isn't enough electrons to cause current to flow, no Ringy-dingy no regeneration, no big bang caused by background radiation or anything else for that matter.

Rich;
If the tube is cut off, it's cut off there must be electrons flowing from cathode to anode for there to be any kind of oscillation.

To address something you brought up several posts back; I have no doubt 90-100MHZ spurs are seen on a spectrum analyzer when you send a series of dits or use a pulser to drive the exciter; the real question is how far below the PEP output of the fundamental are those spurs?

Back in the day I tuned S and L band emitter driven transistor amplifiers, it was extremely difficult to build an amplifier that didn't have some resonant component in the output or input that existed along with the matching networks. You just don't want them to have a very high Q.

And as a bit of trivia;
From what I remember one ampere second is 6.2 x 1023 electrons per second. I could be off by a couple of orders of magnitude however you get the idea you have to knock off a lot of electrons to raise the anode current in a tube, even to raise the tube's anode current by one femto amp. 1 x 10-15 amperes.

One more thing while I am getting ready to head out to the dog show....

Rich;
If by some means electrons get knocked off it's doubtful if there would be any current flowing since for an instant the anode would be more positive than the instant before but since the distance those electrons would have traveled would be so short no plate current would flow as a result of this action. Electrons are in motion all the time in that anode the few that would had been freed would simply add to the random motion of the guzillons of electrons that were in motion at that instant.

Okay see Y'all later off to the dog show.
« Last Edit: October 30, 2011, 10:13:05 AM by AF6LJ » Logged
KA5N
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« Reply #73 on: October 30, 2011, 10:09:44 AM »

If you are fearful of background radiation then just line your shack with lead.
Ought to do the job, and it will match your aluminum foil hat.

Allen
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AG6K
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« Reply #74 on: October 30, 2011, 01:32:45 PM »

Quote
G3RZP
RE: Background Radiation - Could It Be a Vexation ?
« Reply #71 on: Today at 09:53:09 AM »
   
Reply with quoteQuote
One of the old MIL STD Handbooks (might have been 217) had some data on reliability of tubes under irradiation. Since they were irradiating with neutrons in very large speeds and densities, (which would be more likely to knock electrons out) with tubes under power and got very long lives, it seems more than unlikely.

  This thread is not about tube life vs. neutron bombardment.
Rich, ag6k


Quote
In any case, to make the parasitic circuit ring with any amplitude, it will need a pretty large current pulse even with a Q of 10. That is not even a few electrons.
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